The present disclosure relates to a gas turbine engine and, more particularly, to a blade tip rapid response active clearance control (RRACC) system therefor.
Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor to pressurize an airflow, a combustor to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine to extract energy from the resultant combustion gases. The compressor and turbine sections include rotatable blade and stationary vane arrays. Within an engine case structure, radial outermost tips of each blade array are positioned in close proximity to a shroud assembly. Blade Outer Air Seals (BOAS) supported by the shroud assembly are located adjacent the blade tips such that a radial tip clearance is defined therebetween.
When in operation, the thermal environment in the engine varies and may cause thermal expansion and contraction such that radial tip clearance varies. The radial tip clearance is typically designed so that the blade tips do not rub against the Blade Outer Air Seal (BOAS) under high power operations when the blade disk and blades expand as a result of thermal expansion and centrifugal loads. When engine power is reduced, the radial tip clearance increases. The leakage of core air between the turbine blade tips and the BOAS has a negative effect on engine performance/efficiency, fuel burn, and component life. Minimization of this radial tip clearance may be especially complex in a military application due to multiple and rapid throttle excursions. A military engine throttle excursion such as a sudden/snap reaccelerate or hot reburst results in extreme closedown of the radial tip clearance. Conversely, the close down is much less in a cruise condition at which the engine spends the vast majority of its serviceable life.
Due to the extreme closedowns associated with sudden throttle excursions, the turbine is designed to operate with relatively large tip clearance at the high-time steady state cruise conditions which effects overall engine performance/efficiency.